The present invention relates to a device for detecting deformations in pressed members made of sheet metal. The device has a light source which illuminates the pressed member and a receiver (detector) for receiving scattered components of light reflected by the pressed member. The light source and the receiver ar arranged at a fixed known distance from one another and move relative to the pressed member.
In the automobile industry lacquered sheet metal automobile body pieces are taken out of the production process when deformations in the form of minor bulges or dents are visible on the pieces. Such irregularities in the surface, that is, contour irregularities are not discernible by the naked eye before the lacquering process so that a removal of the body pieces from the production process at that time is not readily feasible. In order to select out reject body pieces even before the lacquering phase, the pieces are, for example, roughened manually by filing so that deformations become discernible to the eye as the surface at those locations has become particularly rough or has remained smooth. This procedure is very expensive and has the additional drawback that the entire surface is no longer smooth, but roughened.
A change in the surface is avoided if optical methods are employed. For example, a measuring process is known from the optical measuring art in which bulges or indentations in a surface are made visible by optical means in the form of moire fringes. The surface to be examined in that process is illuminated through a first grid. Components of the light scattered and reflected by the surface are received by a camera through a second grid coordinated with the first grid. Rounded portions (bulges or depressions) in the surface are effectively rendered visible as contour lines, whose density is a measure of the slope of the rounded portion. In order to detect deformations, an actual profile has to be compared with a desired profile. This method is very expensive as two profiles have to be measured simultaneously and subsequent automatic detection is possible only by way of complicated image processing of the two moire fringe patterns.